The present invention relates to reinforced resin compositions comprising a polyethylene terephthalate-type resin as the main component. These resins have excellent heat resistance and are uniform in appearance.
Glass fiber-reinforced polyethylene terephthalate resins have substantial commercial applications because of their excellent mechanical characteristics, chemical resistance and other properties. However, these reinforced resins are still insufficient in various points. For example, when a glass fiber-reinforced polyethylene terephthalate resin is molded at a mold temperature less than 100.degree. C., the heat distortion temperature of the molded articles is as low as about 100.degree. C. and the heat resistance is poor. Furthermore, when a molded article non-uniform in the thickness is prepared, the thin portion is semi-transparent and only the very interior is whitened in the thick portion. In such instances the appearance of the molded article is not uniform and the molded article is not preferred from the aesthetic viewpoint. On the other hand, when the molding operation is carried out at a mold temperature greater than about 120.degree. C., the heat distortion temperature of the molded articles is elevated to a level of approximately 230.degree. C., and even molded articles which have thin portions have a white uniform appearance and excellent gloss properties. This means that when high heat resistance and uniform appearance are required, molding is ordinarily carried out at a high mold temperature, for instance of about 130.degree. to 150.degree. C. On the other hand, high temperature molding has certain limitations and disadvantages, primarily economic, which is a serious drawback from the practical viewpoint.
Metal salts of organic carboxylic acids and inorganic compounds have been found to be effective for improving the heat resistance of polyethylene terephthalate resins. Also, it has been shown that the mold temperature dependence of the heat resistance and appearance in polyethylene terephthalate molded articles can be reduced to some extent by incorporation of these additives. More specifically, even when a polyethylene terephthalate resin containing such additives is molded at a low mold temperature, the degree of whitening in the interior of the thick portion of the resulting molded article is increased and also the heat resistance is improved to some extent. However, when a thin molded article is prepared by low temperature molding, if only an additive such as a metal salt of an organic carboxylic acid or an inorganic compound is incorporated, the heat resistance is still insufficient, the appearance is semi-transparent or the interior is whitened only slightly. Thus a molded article having a uniform appearance cannot be obtained. Particularly in case of a molded article non-uniform in the thickness, the appearance of the thick portion is quite different from that of the thin portion and the molded article is defective from an aesthetic viewpoint.
Starting from this background we made several investigations with a view to developing a resin composition capable of providing a molded article having excellent heat resistance and a relatively uniform appearance--even if the mold temperature is relatively low and the thickness of the molded article is small. As a result we found that these and other objects can be attained by incorporating definite amounts of a specific metal salt of an organic carboxylic acid and a specific ether compound into a glass fiber-reinforced polyethylene terephthalate resin, and that if a specific amount of one or more of liquid paraffins, solid paraffins and polyethylene waxes is incorporated into this resin composition containing the above-mentioned four components, a resin composition is provided having a very excellent, white and uniform appearance and a very high heat resistance. Further, in such compositions the molding temperature dependency and thickness dependency of the heat distortion temperature are substantially reduced.